Cell reselection by a User Equipment UE in a Public Land Mobile Network PLMN between a Time Division-Synchronous Code Division Multiple Access TD-SCDMA system and a Global System of Mobile communication GSM is protocoled.
Serving cell reselection by a UE from the TD-SCDMA system to the GSM is protocoled to be performed according to sorted relative values. Namely, when the signal of a GSM cell is better than that of a serving TD-SCDMA system cell over a continued period of time according to a sorting criterion, cell reselection towards the GSM may be triggered.
Reselection from the TD-SCDMA system to the GSM however depends on an absolute threshold. When a UE camping on the GSM leans by measurement that the signal strength of a TD-SCDMA system cell is higher than the threshold for a continued period of 5 s, cell reselection towards the TD-SCDMA system may be triggered.
It may be understood from the simple description of inter-standard reselection that, due to asymmetric principles in reselection between the GSM and the TD-SCDMA system, there may be chances when both a reselection requirement from a TD-SCDMA system cell to a GSM cell and that from a GSM cell to a TD-SCDMA system cell are met, which may lead to Ping-Pong reselection and thus cause a series of problems as follows, for example. As a UE may receive no paging message during reselection, Ping-Pong reselection may lead to increased paging interruption time. Registration has to be performed after reselection, which no doubt increases a network load, and will lead to UE resource waste, leading to a shortened standby time.